void GPS_NMEA()
{
  while (nmea.available() > 0){
    int c = nmea.read();
    if (gps.encode(c)){
      gps.get_position(&current_loc.lat, &current_loc.lon, &fix_age);  // lat * t6
      current_loc.alt = gps.altitude();  // height in centimeters
      ground_speed = gps.speed();
      ground_course = gps.course();
      if (fix_age == 0xFFFFFFFF){
        GPS_fix = NONE;
      } else if (fix_age > 5000){
        GPS_fix = OLD;
      } else {
        GPS_fix = fix_3D; 
      }
    }
  }
}
